1. Field of the Invention
The present invention relates to a photoelectric conversion element, an image reading device, an image forming apparatus, an image reading method, and a computer-readable recording medium.
2. Description of the Related Art
It has been known that correlated double sampling (CDS) is performed to suppress noises in a photoelectric conversion element such as a complementary metal oxide semiconductor (CMOS) image sensor.
Moreover, Japanese Unexamined Patent Application Publication No. 2006-25189 discloses an image sensor that analog/digital (A/D) converts each of a signal level and a reset level from a pixel portion by an AD converter, and stores the signal level and the reset level in a first register and a second register, and acquires, by an adder, a difference between the level signals respectively in a form of digital signal.
However, there has conventionally been a case in which the difference between the reset level and the signal level varies due to a linearity error of the A/D converter because the reset level to be a reference varies when an offset of a pixel varies. This variation causes remaining a fixed pattern noise, and there has been a problem that a sufficient effect for suppressing noises cannot be produced by CDS. Furthermore, if the signal is amplified after implementing the CDS, there has been a problem that the fixed pattern noise gets worse.
In view of the above problems, there is a need to provide a photoelectric conversion element, an image reading device, an image forming apparatus, an image reading method, and a computer-readable recording medium having a program that enable to improve the noise suppression effect by CDS.